Abstract: Polymer-based thermal conductive composites (PTCs) are crucial for managing heat in microelectronics, yet the impact of filler-filler interfacial thermal resistance (ITR) on their thermal performance remains unclear despite efforts to optimize the filler-matrix interfaces. In this study, the creation of continuous thermal conductive networks with enhanced filler-filler interface contact was achieved in bacterial cellulose/boron nitride nanosheets/MXene composites (BC/BNNS/MXene) by the in-situ coating of silver nanoparticles on the surface of boron nitride nanosheets (Ag@BNNS). The homogeneously dispersed and well-exfoliated BNNS are bridged to each other via the Ag located at the surface of BNNS and a 3D thermal conductive network is formed with solid Ag junctions lying in among. The resulting 3D “branch-leaf” structure significantly enhances thermal conductivity to 18.5 W m^-1 K^-1 at 30 wt.% Ag@BNNS filler loading, and was demonstrated by first-principles simulations, proving that the merged Ag was used as a thermal transport joint to reduce thermal contact resistance within the 3D BNNS and MXene network. Utilizing the MBAg30 composite film as a thermal interface material has been shown to effectively lower the operating temperature of smartphones, reducing it from 33.4 °C to 29.0 °C. The film also demonstrates efficient photothermal conversion, with a surface temperature of 83.6 °C under 100 mW cm^-2 light intensity and a photothermal conversion efficiency of 96.3 %. It demonstrates good stability after seven cycles and can increase ice melting rates in practical applications like agricultural greenhouses and solar heating. The present strategy provides an effective route for developing high-performance PTCs.

Key words: Polymer-based thermal conductive composites, Thermal conduction, Three-dimensional thermal conduction network, Solar thermal conversion, Interface thermal resistance